The natural sense of hearing in human beings involves the use of hair cells in the cochlea that convert or transduce acoustic signals into auditory nerve impulses. Hearing loss, which may be due to many different causes, is generally of two types: conductive and sensorineural. Conductive hearing loss occurs when the normal mechanical pathways for sound to reach the hair cells in the cochlea are impeded. These sound pathways may be impeded, for example, by damage to the auditory ossicles. Conductive hearing loss may often be overcome through the use of conventional hearing aids that amplify sound so that acoustic signals can reach the hair cells within the cochlea. Some types of conductive hearing loss may also be treated by surgical procedures.
Sensorineural hearing loss, on the other hand, is caused by the absence or destruction of the hair cells in the cochlea which are needed to transduce acoustic signals into auditory nerve impulses. People who suffer from sensorineural hearing loss may be unable to derive significant benefit from conventional hearing aid systems, no matter how loud the acoustic stimulus. This is because the mechanism for transducing sound energy into auditory nerve impulses has been damaged. Thus, in the absence of properly functioning hair cells, auditory nerve impulses cannot be generated directly from sounds.
To overcome sensorineural hearing loss, numerous cochlear implant systems—or cochlear prostheses—have been developed. Cochlear implant systems bypass the hair cells in the cochlea by presenting electrical stimulation directly to the auditory nerve fibers by way of one or more channels formed by an array of electrodes implanted in the cochlea. Direct stimulation of the auditory nerve fibers leads to the perception of sound in the brain and at least partial restoration of hearing function.
When a cochlear implant of a cochlear implant system is initially implanted in a patient, and during follow-up tests and checkups thereafter, it is usually necessary to fit the cochlear implant system to the patient. Fitting of a cochlear implant system to a patient is typically performed by an audiologist or the like who utilizes a fitting system to present various stimuli to the patient and relies on subjective feedback from the patient as to how such stimuli are perceived.
The audiologist or the like may further utilize the fitting system to perform diagnostic and/or troubleshooting procedures on a cochlear implant system. For example, if a cochlear implant system stops working correctly, the fitting system may be utilized to troubleshoot the cochlear implant system. During troubleshooting, a cochlear implant emulation device may be substituted for an implanted cochlear device in the cochlear implant system in order to determine whether the implanted cochlear implant is the source of a problem. This is typically accomplished by the audiologist or the like uncoupling the implanted cochlear device from a component of the cochlear implant system and coupling a cochlear implant emulation device configured to emulate the implanted cochlear device to the component.
A cochlear implant emulation device typically includes an implantable cochlear device bundled with a resistive load intended to help the implantable cochlear device emulate conditions of an implanted cochlear implant device. Because the cochlear implant emulation device is designed to operate as much like an implanted cochlear implant device as possible, a conventional fitting system is unable to distinguish the cochlear implant emulation device from the implanted cochlear implant device. While this is a desirable characteristic for diagnosing and/or troubleshooting the cochlear implant system, the inability of the fitting system to distinguish between the cochlear implant emulation device and the implanted cochlear implant device can undesirably affect certain operations of the fitting system. For example, patient data maintained by the fitting system may be inadvertently polluted with data gathered from and representative of characteristics (e.g., impedance values) of the cochlear implant emulation device. Unfortunately, because the characteristics of the cochlear implant emulation device may be different from characteristics of the implanted cochlear implant device, once data gathered from the cochlear implant emulation device is mingled with the patient data, the characteristics of the cochlear implant emulation device will undesirably affect computations performed by fitting subsystem, such as computations performed to fit the implanted cochlear implant device to a patient.